JP2001133679A - Electronic camera and automatic focusing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electronic camera which can continuously take out picture from a semiconductor imaging device, while realizing phase difference AF(automatic focusing) and contrast AF on the same semiconductor imaging device. SOLUTION: This electric camera divides a luminous flux from an object into two optical paths by a light separation part 29 and adjusts optical axes of two optical paths, approximately in parallel with each other by a mirror 30. A pupil separator lens 31 is provided on one optical path to re-focus an object image on the same plane as an object image-forming position on the other optical path. A first photodetector area, where not only an object image is photographed but also this object image is focused on by a contrast AF system and a second photodetector area, where the object image formed by the pupil separator lens 31 is used to focus on the object image to be photographed in the first photodetector area by a phase difference AF system are set on a semiconductor element 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic camera for photographing using a semiconductor image pickup device such as a CCD two-dimensional image sensor and an automatic focusing method of the electronic camera, and more particularly to an electronic camera on the same semiconductor image pickup device. The present invention relates to an electronic camera capable of continuously extracting images from a semiconductor image pickup device while realizing automatic phase difference focusing and automatic contrast focusing, and an automatic focusing method for the electronic camera.

[0002]

2. Description of the Related Art In recent years, a subject image is formed on a semiconductor imaging device, for example, a CCD two-dimensional image sensor by an imaging optical system and converted into an electric signal. A so-called electronic camera that records data on a recording medium such as a disk has been widely used.

Most electronic cameras of this type are equipped with an autofocus (AF) mechanism for controlling photographing conditions to automatically focus a subject image.
A method called contrast AF or hill-climbing AF is often used for the F mechanism. This is CC for imaging
This is because the D output can be used for AF as it is. More specifically, in this contrast AF method, the contrast value (A
F evaluation value), and focuses on the maximum value.

On the other hand, in a silver halide camera, in addition to the contrast AF, a phase difference AF method is widely used. In the phase difference AF method, two pupils are provided on an optical path to divide a light beam from a subject, and both light beams are respectively imaged on an image sensor. Then, it is determined whether or not the subject is in focus by examining the shift of the image forming position.

[0005] These two AF methods are widely used in silver halide cameras, but each has its advantages and disadvantages. FIG. 7 is a diagram for comparing advantages and disadvantages of the phase difference AF and the contrast AF.

As shown in FIG. 1, in the phase difference AF, it is difficult to focus on a subject having a repetitive pattern such as vertical stripes.
Is generally limited to one point. On the contrary,
In contrast AF, it is possible to effectively focus even on a repetitive pattern, and the target point of AF can be regarded as a surface having a spread.

Further, in the phase difference AF, the amount of movement of the AF lens is determined by the shift of the image forming position in the image sensor, so that the AF range (AF range) is limited depending on the image sensor and lens system. Therefore, when the range from infinity to the closest distance is large, if the lens system is set so that AF can be performed in all photographable ranges, CC
The resolution may be reduced due to the balance with the D element size and the AF accuracy may be reduced. On the other hand, in contrast AF, an AF target is measured on a surface, and a contrast value is obtained. Therefore, the AF range is wide, and the AF accuracy is not particularly lowered in consideration of the AF range.

Conversely, in the phase difference AF, the focusing speed is high.
In the phase difference AF, the AF is performed by shifting the imaging position of the subject image.
This is because the amount of movement of the lens can be determined. On the other hand, in contrast AF, unless the contrast value is compared by moving the AF lens, it cannot be determined whether the focus state is good or bad. That is, since focusing is performed by repeating lens movement and evaluation, the focusing speed is slow in contrast AF. In particular, when a zoom lens is used, the maximum AF step becomes very large in consideration of macro shooting.

As described above, since it takes time for focusing in contrast AF, for example, Japanese Patent Laid-Open No. Hei 9-18195
A technique for realizing phase difference AF in an electronic still camera, such as that disclosed in Japanese Unexamined Patent Publication (Kokai) No. 4 (1994), has been devised.
In Japanese Patent Application Laid-Open No. Hei 9-181954, pupil time-division phase difference AF is performed by a single CCD element by providing pupil position moving means combining a pupil stop and a light shielding plate. Also, in the CCD, the contrast A
The F method is also possible, and the phase difference AF and the contrast AF can be switched and used.

On the other hand, with the recent improvement in semiconductor technology, the number of pixels of a semiconductor imaging device used in an electronic camera has been increasing. Conventionally, as a moving image, 30 to 40
A CCD having about 1 million pixels and a CCD of about 1 to 2 million pixels has been used for still images. Recently, however, the number of pixels for still images has exceeded 2 million pixels. However, with the increase in the number of pixels of the CCD, there is a problem that it takes time to read data from the CCD. In addition, due to an increase in the amount of information accompanying an increase in the number of pixels, processing after reading is also taking time. Therefore, in the contrast AF method in the electronic camera, the focusing time becomes longer.

Recently, in electronic still cameras,
There is a tendency that a model that can shoot not only a still image but also a moving image has appeared, and that a CCD output is displayed on a finder and used as an electro view finder (EVF). However, if a CCD having a large number of pixels is used, it takes time to read data, and it is difficult to secure a general moving image display speed of 30 frames / second.

[0012]

In the system disclosed in Japanese Patent Application Laid-Open No. 9-181954, the concept of taking an image after focusing by the AF mechanism is taken.
D is used at each time either as a sensor for AF or as an element for photography. That is, C
It is not possible to obtain an image output from the CCD while performing the AF operation using the CD.

As described above, in recent years, utilization of a CCD output as an EVF has been studied. However, if the CCD output is used as EVF,
It is necessary to continuously take out images.
It is difficult to achieve this by the method of 81954.

The present invention has been made in view of such circumstances, and has a phase difference A on the same semiconductor imaging device.
It is an object of the present invention to provide an electronic camera capable of continuously extracting an image from the semiconductor imaging device while realizing F and contrast AF, and an automatic focusing method of the electronic camera.

[0015]

In order to achieve the above-mentioned object, an electronic camera according to the present invention includes a light receiving element region of a contrast AF system and a phase difference A on a single semiconductor image pickup device.
By providing an F-type light receiving element region, both a contrast AF and a phase difference AF can be performed by a single semiconductor image pickup device. Therefore, a light flux from a subject is transmitted to two optical paths. A light splitting means for splitting and adjusting the optical axes of the two split optical paths so as to be substantially parallel to each other; and providing an image of a subject in one of the two optical paths and the other of the two optical paths. A pair of lenses for re-imaging the subject image on the same plane as a position, and a surface-reception type AF semiconductor imaging element in which a light-receiving element is arranged corresponding to the two subject image forming positions; The AF semiconductor imaging device captures the subject image, and a first light receiving element region for focusing the captured subject image by a contrast automatic focusing method. And a second light receiving element region for focusing the object image photographed in the first light receiving element region by the phase difference automatic focusing method using the object image formed by the phase shift. I do.

In the electronic camera according to the present invention, the phase difference AF and the contrast AF are realized on the same semiconductor image pickup device, so that, for example, an advantageous AF depending on the situation is provided.
In addition, since the two light receiving element regions are clearly separated from each other, it is possible to obtain an image output while performing the AF operation.

Further, the electronic camera according to the present invention includes the AF which receives a light beam from the subject for photographing a still image.
A surface light receiving type still image semiconductor imaging device having a larger number of light receiving elements than a semiconductor imaging device is divided into an optical path for allowing a light beam from the subject to enter the semiconductor imaging device and an optical path for allowing the light beam to enter the still image semiconductor imaging device. It is preferable to include a second light splitting unit.

In the electronic camera according to the present invention, two semiconductor image pickup devices are provided, an output from the semiconductor image pickup device having a small number of light receiving elements is used for determining AF conditions, and an output from the semiconductor image pickup device having a large number of light receiving elements is used. When used for recording a still image, it is possible to achieve both fast AF and high-quality still image shooting.

Further, the electronic camera according to the present invention is characterized in that the AF
It is preferable to use an output from the first light receiving element region of the semiconductor image pickup device for displaying an image or recording a moving image of an electroviewfinder.

In the case of EVF or moving image recording, high image quality is not always required as in still image shooting. Therefore, in the electronic camera of the present invention, by using the output from the semiconductor imaging device having a small number of light receiving elements for EVF and moving image recording,
Irrespective of the increase in the number of pixels of a still image, continuous image extraction can be performed without interrupting EVF or moving image recording.

The automatic focusing method applied to the electronic camera according to the present invention includes a first focusing step of performing automatic focusing by a phase difference automatic focusing method, and a focusing result of the first focusing step. A moving range determining step of determining a moving range of the automatic focusing lens in the contrast automatic focusing,
A second focusing step of performing automatic focusing by the contrast AF method within the lens moving range determined in the moving range determining step.

In general, in the phase difference AF method, the amount of shift from the in-focus position can be determined, so that high-speed AF can be performed. On the other hand, if the range from infinity to the closest distance is large due to the size of the lens system and the size of the semiconductor imaging device, The resolution may decrease and the AF accuracy may decrease. On the other hand, in the contrast AF method, in principle, a subject at any distance can be focused, but on the other hand, it takes a long time to focus because the hill-climbing step is performed. Therefore, in the automatic focusing method of the present invention, first, focusing is performed by the phase difference AF, a hill-climbing step range in the contrast AF is narrowed based on the focusing result, and the contrast AF is performed within the narrowed range. . Thereby, high-speed and high-precision AF is realized.

[0023]

An embodiment of the present invention will be described below with reference to the drawings. (First Embodiment) First, a first embodiment of the present invention will be described.

FIG. 1 is a device configuration diagram of the electronic camera according to the first embodiment. In this electronic camera, a moving image CCD (mCCD: about 300,000 pixels) 5 is passed through a lens system 1, an AF mechanism 2, an aperture 3, and a spectral unit 4, and an infrared cut filter is provided from the spectral unit (beam splitter) 4. (Not shown), a still image CCD (sCC
D: 2 million pixels or more). At the time of reading from the sCCD 7, the shutter 6 is closed. The shutter 6 is a mechanical focal plane shutter.

The output of the sCCD 7 is an image pickup circuit (exposure, readout, element shutter control, sCCD power supply on / off control, etc.) 8, an A / D converter 9, a still image processing unit (conversion to still image information for photographs, etc.) (XGA, etc.)) and then temporarily stored in the buffer memory 11. The photographed image is output from the buffer memory 11 by the display control unit 12 from the liquid crystal panel (for reproduction) 13 on the back, and when the image is stored, the image is compressed by JPEG by the compression / expansion unit 14 to a magneto-optical disc drive (magnetic floppy disk,
HDD), semiconductor memory (flash memory) or the like) 15. The output from the magneto-optical disk drive 15 is displayed after being expanded and stored in the buffer memory 11. The sCCD 7 is normally turned off to save power, and is turned on when the first release is turned on.

On the other hand, the output of the mCCD 5 is
6, an A / D converter 17, a moving image processing unit 18, a VRAM (video RAM) 19, and an EVF by a display control unit 20.
Liquid crystal panel (looking type EVF) 2
It is displayed from 1. The above-described display of a still image is a so-called RE
C view (display of recorded image)
The output display from the CD 5 is a display as an EVF (Electro View Finder). That is, mC
The output from the CD 5 is first used for a finder. The output from mCCD5 is stored in buffer memory 2
2. Magneto-optical disk drive 1 via compression / decompression unit 23
5 as a moving image. Motion JPEG is used as the compression / decompression method. The recorded video is
It can be reproduced from the rear liquid crystal panel in the same manner as a still image.

The output from the mCCD 5 is input from the A / D converter 17 to the system controller 24,
The F control unit 25 uses the phase difference AF method and the contrast AF (hill climbing AF) AF control.

The system controller 24 controls each unit in the camera as shown by the arrow in FIG. 1 and receives various operation inputs from various operation buttons 26. The AF controller of the system controller 24 includes the A / D converter 1
The AF mechanism is controlled on the basis of the output from the mCCD 5 via. The AF method is a contrast AF and a phase difference AF. How to use these two AF methods will be described later.

FIG. 2 shows the mCC after the spectroscopic unit 4 shown in FIG.
FIG. 3 is a diagram illustrating an optical system of D5, and FIG. 3 is a diagram illustrating an example of a light receiving element arrangement of the mCCD5. One of the light beams split by the light splitting unit 4 passes through the shutter 6 and
It is incident on D7. The other light beam enters the second beam splitter 29 via the mirror 27 and the optical path length adjusting lens 28. Here, the optical path length adjusting lens 28 is for adjusting the optical path length so that the subject is simultaneously focused in the imaging areas of the sCCD 7 and the mCCD 5. Note that a single prism may be provided instead of the light splitting unit 4 and the mirror 27.

One of the light beams split by the second beam splitting unit 29 directly enters the imaging area of the mCCD 5 shown in FIG. This incident provides a through image for EVF, and the output from the area is a contrast AF.
Used for

The other light beam split by the second beam splitting unit 29 is made parallel to the one light beam by a mirror 30, and furthermore, a phase difference AF sensor in the mCCD 5 shown in FIG. The light enters the area a2. This phase difference AF sensor area a2 is
1 is provided at the end of the mCCD 5 so as not to interfere with the operation. In FIG. 3, the imaging area a1 and the two phase differences AF
Although three light receiving element regions with the sensor region a2 are shown, these are actually light receiving element regions that are continuously integrated, and are merely assigned roles. As a modification, the three light receiving element regions may be configured as separate light receiving element regions on the same device.

Further, as shown in FIG. 4, the pupil separator lens 31 of the light beam reflected by the second
This is a pair of lenses for taking out different parts and dividing the pupil, and each light beam split by the second spectral unit 29 is mCC
It also has the role of adjusting the optical path length so that an image is formed on the same plane of D5. Note that the optical path length adjustment here may be such that an optical path length adjustment lens (not shown) is provided between the second beam splitting unit 29 and the pupil separator lens 31.

FIG. 4 is a diagram showing how the phase difference AF is performed using the output of the phase difference AF sensor area in the mCCD 5. As shown in the figure, sCCD7 and mCCD5
Is located at a position where the subject image is optically focused and formed in the same manner.

In the phase difference AF, as shown in FIG. 4, the degree of focus (shift amount) and the shift direction are determined based on the relative difference between the image forming positions of the left and right sensors. Next, the operation of the electronic camera according to the first embodiment will be described with reference to FIG. FIG. 5 is a flowchart for explaining the operation of the electronic camera of the first embodiment.

In this electronic camera, when the photographing mode is set (YES in step A1), first, AF processing by the phase difference AF method is executed (step A2). If focus is achieved here (YES in step A3), this processing is terminated. For example, the point to be focused is out of the measurable area of the phase difference method, or the focus target cannot be focused due to vertical stripes or the like. In this case (NO in step A3), focusing by the contrast AF method is executed (step A4).
Step A5). During this time, the through image from the mCCD 5 is continuously provided to the EVF 21, and continuous EVF display is realized.

As described above, in the electronic camera of the first embodiment, high-precision still image shooting can be performed by the sCCD 7, and high-speed moving image shooting and continuous EVF display can be performed by the mCCD 5.

That is, first, A is determined by the phase difference AF method.
Since the F processing is performed, high-speed AF can be performed.
Is performed, a reliable focusing can be realized.

(Second Embodiment) Next, a second embodiment of the present invention will be described. The electronic camera according to the second embodiment has the same configuration as the electronic camera according to the first embodiment shown in FIG. The electronic camera of the first embodiment is different from the electronic camera of the first embodiment in that a second image is formed on the phase difference AF sensor so that the subject is reliably imaged from infinity to the shortest possible distance.
The optical system after the spectroscopy unit is constituted. That is,
In the electronic camera of the first embodiment, A
Although the optical system and the phase difference AF sensor are arranged with priority given to the F accuracy, in the second embodiment, the optical system and the phase difference A are given priority given to the effective range of the AF measurable range (range).
An F sensor is arranged. In contrast AF, the AF accuracy is prioritized over the AF focusing speed, and the area of the AF evaluation area is set to be relatively large.

As described above, in the second embodiment, for the phase difference AF, the size of the focusable range is given priority over the accuracy, and for the contrast AF, the focusing accuracy is given priority over the focusing speed. Has been adjusted as follows.

The AF controller 25 of the system controller 24 is provided with a process for determining the range in which the contrast AF is to be performed based on the result of the phase difference AF.
That is, the AF control unit 25 holds the correspondence information between the moving range of the AF lens and the subject distance. When the subject distance is known by the phase difference AF, only the predetermined range before and after the subject distance is subjected to the contrast AF (the range where the contrast AF is performed). This is determined as a range in which the AF lens is moved in the hill climbing step.

The operation of the electronic camera according to the second embodiment will now be described with reference to FIG. FIG. 6 is a flowchart illustrating the operation of the electronic camera according to the second embodiment.

In the electronic camera, when the photographing mode is set (YES in step B1), first, AF processing by the phase difference AF method is executed (step B2). If the image is out of focus (for example, vertical stripes) (NO in step B3), the hill-climbing step range in the contrast AF is set to the AF lens movable range (from infinity to the closest photographable position) (step B4), and the contrast AF is performed. Move on to processing.

On the other hand, when focusing is performed by the phase difference AF (YES in step B3), it is further determined whether or not the high-precision AF mode is set (step B5). (NO in B5), this process ends. The high accuracy mode is turned on / off by a notification from the operation button 26 to the system controller.

In the high-precision AF mode (step B
5), a hill-climbing step range is determined based on the subject distance measured by the phase difference AF so that the AF step is performed for a certain distance before and after the subject distance (step B6).
Then, the contrast AF is executed in this range (step B7, step B8).

As described above, in the electronic camera according to the second embodiment, high-speed and high-precision AF is realized by a combination of the two AF methods, the phase difference AF method and the contrast AF method.

[0046]

As described above in detail, according to the present invention, since the light receiving element region of the contrast AF method and the light receiving element region of the phase difference AF method are provided on one semiconductor image pickup device, the same structure is provided. By realizing the phase difference AF and the contrast AF on the semiconductor image sensor, for example, it is possible to use an advantageous AF depending on the situation, and the two light receiving element regions are clearly separated. In addition, it is possible to obtain an image output while performing the AF operation.

Further, two semiconductor image pickup devices are provided, and the output from the semiconductor image pickup device having a small number of light receiving elements is used for determining AF conditions, and the output from the semiconductor image pickup device having a large number of light receiving elements is used for recording a still image. This makes it possible to achieve both fast AF and high-quality still image shooting.

In consideration of the fact that EVF or moving image recording does not necessarily require high image quality as much as still image shooting, the output from a semiconductor imaging device having a small number of light receiving elements is used for EVF or moving image recording. Irrespective of the increase in the number of pixels of a still image, continuous image extraction can be performed without interrupting EVF or moving image recording.

Further, in general, in the phase difference AF method, the amount of shift from the in-focus position can be determined, so that the AF can be performed at high speed. On the other hand, the range from infinity to the closest distance depends on the size of the lens system and the size of the semiconductor imaging device. If the resolution is large, the resolution may decrease, and the AF accuracy may decrease. On the other hand, in contrast AF, in principle, a subject at any distance can be focused, but a hill climbing step is performed, so that it takes time to focus. In consideration of this, first, focusing is performed by the phase difference AF, the hill-climbing step range in the contrast AF is narrowed based on the focusing result, and the contrast AF is performed within the narrowed range, thereby achieving high-speed and high-precision AF. Realize.

[Brief description of the drawings]

FIG. 1 is a device configuration diagram of an electronic camera according to a first embodiment of the present invention.

FIG. 2 is a view showing m and subsequent parts of the electronic camera according to the first embodiment;
The figure which shows the optical system of CCD.

FIG. 3 is a view showing an example of the arrangement of light receiving elements of the mCCD of the electronic camera according to the first embodiment.

FIG. 4 is a diagram showing a state in which phase difference AF is performed using an output of a phase difference AF sensor area in the mCCD of the electronic camera of the first embodiment.

FIG. 5 is a flowchart for explaining the operation of the electronic camera of the first embodiment.

FIG. 6 is a flowchart illustrating the operation of the electronic camera according to the second embodiment.

FIG. 7 is a diagram for comparing advantages and disadvantages of a phase difference AF and a contrast AF.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Lens system 2 ... AF mechanism 3 ... Aperture 4 ... Spectroscopic part 5 ... CCD for moving image (mCCD) 6 ... Shutter 7 ... CCD for still image (sCCD) 8 ... Imaging circuit 9 ... A / D converter 10 ... Still image Processing unit 11 Buffer memory 12 Display control unit 13 Rear liquid crystal panel 14 Compression / expansion unit 15 Magneto-optical disk drive 16 Imaging circuit 17 A / D converter 18 Video processing unit 19 VRAM (video RAM) Reference Signs List 20 display control unit 21 EVF liquid crystal panel 22 buffer memory 23 compression / expansion unit 24 system controller 25 AF control unit 26 operation button 27 mirror 28 optical path length adjustment lens 29 second spectral unit 30 Mirror 31: Pupil separator lens

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H04N 5/335 G03B 3/00 A

Claims (4)

[Claims] 1. A light splitting means for splitting a light beam from a subject into two optical paths and adjusting the optical axes of the two split optical paths so as to be substantially parallel to each other, and one of the two optical paths. A pair of lenses provided on the same optical path and re-imaging the subject image on the same plane as the subject image forming position on the other optical path; and a light receiving element is arranged corresponding to the two subject image forming positions. A self-focusing semiconductor imaging device of a surface light receiving type, wherein the self-focusing semiconductor imaging device captures the subject image and focuses the captured subject image by a contrast automatic focusing method. A first light-receiving element region, and a second light-receiving element for focusing the subject image photographed in the first light-receiving element region by a phase difference automatic focusing method using the subject image formed by the pair of lenses. An electronic camera, characterized in that it comprises a light receiving element region. 2. A surface-receiving type still image semiconductor imaging device having a larger number of light-receiving elements than the self-focusing semiconductor imaging device for receiving a light beam from the object for photographing a still image, and a light beam from the object. 2. The electronic camera according to claim 1, further comprising: a second light splitting unit that splits the light into an optical path for entering the semiconductor image pickup device and an optical path for entering the still image semiconductor image pickup device. 3. The electronic camera according to claim 2, wherein an output from the first light receiving element region of the self-focusing semiconductor image pickup device is used for displaying an image on an electro-viewfinder or recording a moving image. 4. An automatic focusing method applied to the electronic camera according to claim 1, wherein: a first focusing step of performing automatic focusing by a phase difference automatic focusing method; A moving range determining step for determining a moving range of the automatic focusing lens in the contrast automatic focusing based on a focusing result of the first focusing step; and a contrast AF method within the lens moving range determined in the moving range determining step. And a second focusing step of performing automatic focusing according to (1).